TOPS-20 PASCAL Language Manual - Bitsavers

PASCAL DATA TYPES
Example 2
VAR Cit~_Census : PACKED ARRAY [1 •• 25J OF 2500 •• 50000;
J : I NTEGEF: i;
BEGIN
FOI:< I: : :~: :L TO 2~:.:j DO
C 1. t ~~ .... C (.:~ n sus I:: I] ! :=: ();
END;
This example declares the variable City Census as a 25-element array
of integer values in the subrange from ~500 through 50000. A value of
a is assigned to each element of the array.
2.6 TYPE COMPATIBILITY
Type compatibility rules determine the operations and assignments that
you can perform with data items of different types. Two scalar types
are compatible if their type identifiers are declared equivalent in
the TYPE section. In addition, a subrange type is compatible with its
base type, and two subranges of the same base type (or equivalent base
types) are compatible.
For structured and pointer types, PASCAL enforces structural
compatibility. Two structured (that is, arrays, records, files, and
sets) or pointer types are compatible if their structures are
identical.
The way PASCAL determines structural compatibility depends
types involved. For instance, the requirements for
compatibility differ from those for array compatibility.
on the
record
PASCAL uses compatibility rules in the fo]lowing three contexts:
1. Expression compatibility
2. Assignment compatibility
3. Formal and actual parameter compatibility
Expression compatibility determines the types of operands you can
in an expression. See Chapter 3 for information on expressions.
use
Assignment compatibility determines the types of values you can assign
to variables of each type. Assignment compatibility rules apply to
value initializations, assignment statements, and value parameters.
Assignment compatibility is described with the assignment statement in
Section 5.2.
Formal and actual parameter compatibility determines the types of data
you can pass in a parameter list. Value parameters follow the rules
for assignment compatibility. Variable parameters follow somewhat
different rules. Value and variable parameters are described in
Chapter 6.
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